Fuel cells are used to produce electricity when supplied with fuels containing hydrogen and an oxidant such as air. A typical fuel cell includes an ion conductive electrolyte layer sandwiched between an anode and a cathode. There are several different types of fuel cells known in the art, one of which is known as a solid oxide fuel cell or SOFC.
In a typical SOFC, an oxidant, for example air, is passed over the surface of the cathode and a fuel containing hydrogen is passed over the surface of the anode opposite that of the cathode layer. Oxygen ions from the air migrate from the cathode layer through the dense electrolyte layer in which it reacts with the hydrogen and CO in the fuel, forming water and CO2 and thereby creating an electrical potential between the anode layer and the cathode layer of about 1 volt.
Each individual SOFC is mounted within a metal frame, referred to in the art as a retainer, to form a cell-retainer frame assembly. The individual cell-retainer frame assembly is then joined to a metal separator plate to form a fuel cell cassette. In order to produce a voltage sufficiently high to be used in a variety of applications, the cassettes are stacked in series to form a fuel cell stack.
Each fuel cell cassette includes a cathode interconnect which serves to define a flow passage which allows the oxidant to flow across the cathode. The cathode interconnect also serves to provide electrical communication from the cathode to an adjacent fuel cell cassette. In order to ensure an adequate electrical contact between the cathode and the cathode interconnect, an electrically conductive material is typically provided between the cathode and the cathode interconnect. However, electrically conductive materials which are functionally effective and cost effective may be subject to volatizing due to the high operating temperatures that are experienced and due to the oxidant flow which comes into contact with the electrically conductive material. Consequently, the electrically conductive material may lose functionality over the life of the fuel cell stack which may result in unfavorable performance.
Similarly, each fuel cell cassette includes an anode interconnect which serves to define a flow passage which allows the fuel to flow across the anode. The anode interconnect also serves to provide electrical communication from the anode to an adjacent fuel cell cassette via the separator plate. In order to ensure an adequate electrical contact between the anode and the anode interconnect, an electrically conductive material is typically provided between the anode and the anode interconnect. However, electrically conductive materials which are functionally effective and cost effective may be subject to volatizing due to the high operating temperatures that are experienced and due to the fuel flow which comes into contact with the electrically conductive material. Consequently, the electrically conductive material may lose functionality over the life of the fuel cell stack which may result in unfavorable performance.
What is needed is a fuel cell stack and a method which minimizes one or more of the shortcomings as set forth above.